Spring Integration 5.1 - integration flow test - dsl - spring-integration

Question

I have set up a simple Spring Integration flow which is composed of such steps:
poll a rest api periodically then
do some processing on the payload
and land it on a Kafka topic.
Please observe the code below:
#Component
public class MyIntegrationFlow extends IntegrationFlowAdapter {
#Override
protected IntegrationFlowDefinition<?> buildFlow() {
return from(() -> List.of("pathVariable1", "pathVariable2"), c -> c.poller(Pollers.fixedDelay(5, TimeUnit.SECONDS)))
.split()
.handle(httpRequest(), c -> c.advice(new RequestHandlerRetryAdvice()))
.transform(Tranformers.fromJson(Foo.class))
.filter(payload -> payload.isValid())
.log()
.transform(Tranformers.toJson())
.channel(Source.OUTPUT); // output channel for kafka topic
}
private HttpMessageHandlerSpec httpRequest() {
return Http.outboundGateway("http://somehost:8080/{pathVariable}")
.httpMethod(GET)
.uriVariable("pathVariable", Message::getPayload)
.expectedResponseType(String.class);
}
}
This works brilliantly, however, I am struggling to come up with some good tests.
How am I supposed to mock the external REST API?
How am I supposed to test that the retry policy does kick in and the desired number of http requests are made?
How do I change the MessageSource of the flow (list of path vars) that is polled periodically?
How do I check if the payload has successfully made it to the Kafka topic?

Answer 1

Too much questions and some of them requires too broad explanation. Anyway I think you can start from Spring Integration Testing Framework and its documentation.
How am I supposed to mock the external REST API?
I think you can just consider to use a Mock MVC from Spring Framework and its MockMvcClientHttpRequestFactory to inject into the HttpRequestExecutingMessageHandler based on the HttpMessageHandlerSpec.
retry policy does kick
Well, I guess the same mocked MVC endpoint can verify how many times it has been called and fail for first several times to initiate that retry.
How do I change the MessageSource
This is exactly a part of Spring Integration Testing Framework with its MockIntegration.mockMessageSource() and MockIntegrationContext: https://docs.spring.io/spring-integration/docs/5.1.6.RELEASE/reference/html/#mockintegration
made it to the Kafka topic?
Or you the mentioned MockIntegration.mockMessageHandler() to verify that endpoint for Kafka is called. Or use an Embedded Kafka from Spring Kafka project: https://docs.spring.io/spring-kafka/docs/2.2.7.RELEASE/reference/html/#embedded-kafka-annotation